As technologies evolve, complementary metal-oxide semiconductor (CMOS) image sensors attract more and more attention due to their performance advantages. For example, CMOS image sensors can provide higher image acquisition rates, lower operating voltages, lower power consumption and greater noise immunity. A CMOS image sensor typically comprises an array of light-sensing elements or pixels. Each of the pixels is configured to convert received photons into electrons. Additionally, the CMOS image sensor comprises circuitry to transform the electrons into electrical signals. The electrical signals are then processed to generate an image of a subject scene.